Flow meters are used to ascertain the air flow in the intake tract and the charge tract of an internal combustion engine. Since the weight ratios are important in the chemical process of combustion, the mass flow rate of the intake/charge air is to be measured, for which volume measuring methods or impact pressure measuring methods are used to some extent.
Various types of sensors are known for measuring the air mass throughput. One such type of sensor is the so-called hot-film mass airflow sensor, such as that described in one possible specific embodiment in German Published Patent Application No. 103 45 584. The flow meter according to German Published Patent Application No. 103 45 584 has a sensor housing, having a cavity, for accommodating an electronic module, which is separated from a bypass-measuring channel. The electronic module here has a support profile, which is formed essentially on a bottom plate having side webs molded on the opposing longitudinal sides. The electronic module also has a plastic support tongue, which is situated on one of the head sides of the support profile and accommodates the sensor element. A circuit board equipped with electronic components and printed conductors is usually attached to the bottom plate of the support profile to provide an evaluating electronic unit.
German Published Patent Application No. 103 45 584 also describes how the electronic module is held by the side webs in the cavity provided here after being inserted into the sensor housing, while achieving a clamping effect. The molded sensor receptacle here protrudes into the bypass measuring channel through an outlet opening between the latter and this cavity.
With advances in the field of hot-film mass airflow sensors, the evaluation circuits implemented on the circuit board due to the expansion of same with more and more functions have become increasingly more complex, so that these requirements cannot be met merely by a denser configuration of the electronic components alone in the case of an assembly surface having a limited surface area. A double-sided assembly on both the top and bottom sides of the circuit board is thus necessary, while the size of the installation space and the assembly area remain the same.
Openings in the bottom plate of the support profile, through which the electronic components situated on the bottom side of the circuit board may protrude, have been provided previously. However, the stiffness of the construction is reduced by this opening and the stability in the alternating thermal stress load decreases. Furthermore, an additional cover or seal of the electronic components passing through the openings on the back side of the support profile is necessary. This has disadvantageously resulted in a restricted lifetime of the electric connections.